Cutting inserts described in Japanese Unexamined Patent Application Publication No. H10-505012A (Patent Document 1), Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-502874A (Patent Document 2), and Japanese Unexamined Patent Application Publication No. 2009-12116A (Patent Document 3) are known as cutting inserts for use in turning processing of a work material. For example, with the cutting insert described in Patent Document 3, a cutting edge portion is formed at an end portion of an insert body that elongates in a longitudinal direction. A front cutting edge and a lateral cutting edge are formed in the cutting edge portion. A top surface that functions as a rake surface is formed unevenly and, as such, the lateral cutting edge is also formed unevenly and matches the shape of the rake surface.
In order to avoid interference between a holder and the work material when attaching the cutting insert to the holder and performing grooving, a width, in a direction orthogonal to the longitudinal direction, at a portion where a bottom surface side of the cutting insert is held in the holder, is formed narrower than a width of the front cutting edge in this direction. Consequently, there are cases where the rigidity of the holder is insufficient and chatter vibration occurs.
In the cutting insert recited in Patent Document 3, a portion of the lateral cutting edge located at a front side is inclined with ascending as getting away from the front cutting edge. As a result of being inclined in this manner, a direction of cutting resistance applied to a region of the rake surface along this portion is not directed in a direction directly below, but rather is applied in a direction inclined toward the rear side. Accordingly, it is easier to stably hold the cutting insert in the holder.
As a result of the lateral cutting edge being inclined in the manner described above, it is easier to disperse forces applied to the cutting insert to the rear side. However, in cases where the lateral cutting edge is inclined greatly, while it is easier to disperse the forces to the rear side, forces applied from the lateral cutting edge on the chip so as to push back to the front side become greater. Consequently, in cases where a thickness of the chip is thin, there is a possibility of the chip being pushed back to the front side and chip jamming occurring.
In light of the problems described above, an object of the present invention is to provide a cutting insert that can be stably held in a holder and can stably process chips; a cutting tool; and a method for manufacturing a machined product.